The disclosure of Japanese Patent Application No. 11-252593 filed on Sep. 7, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a motor drive unit which controls an electric motor through pulse width modulation (PWM) control and to detection of a malfunction for the motor drive unit.
2. Description of the Related Art
At present, there is a motor drive unit which controls an electric motor. The motor drive unit has a bridge circuit composed of four sides that each have a switching element. The electric motor has at least two ends connected to the switching elements that are diagonally positioned in relation to the bridge circuit. At least one of the switching elements is connected to a power line, and at least one of the other switching elements is grounded. The motor unit is driven by applying voltage to the power switching element. By performing pulse width modulation control of the switching elements, drive control of the electric motor is performed. In a drive unit of this type, if the sum of the terminal voltages of the electric motor becomes approximately equal to xe2x80x9c0xe2x80x9d, i.e., equal to or smaller than a predetermined threshold value (e.g. approximately 3% of the battery voltage), it is determined whether or not the electric motor and the grounded line has been short-circuited (e.g. Japanese Patent Application Laid-Open No. 5-185937).
However, the aforementioned motor drive unit takes into account nothing but the possibility of the portion between one terminal of the electric motor and the grounded line being short-circuited. Therefore, this motor drive unit is useless when there is a malfunction occurring in a motor drive device, a malfunction detection controller, or the like.
The invention provides a motor drive unit and a method of detecting a malfunction thereof which make it possible to detect a wide variety of malfunctions relating to an electric motor by detecting various malfunctions in the electric motor, the motor drive device and the malfunction detection monitor device.
To achieve the aforementioned and/or other objects, a motor drive unit in accordance with a first exemplary embodiment of the present invention has a bridge circuit composed of four sides that each have a switching element. An electric motor having two ends is connected to the bridge circuit that is diagonally positioned in relation to the electric motor. At least one of the pair of switching elements is connected to a power line, and at least one of the other switching elements is grounded. The motor drive unit is driven by applying voltage to the power terminal. By performing pulse width modulation control of the switching elements, drive control of the electric motor is performed. The motor drive unit has a malfunction judgment controller which judges the occurrence of a malfunction when the sum of the terminal voltages of the electric motor is different from a power voltage by a predetermined value or more during operation of the electric motor.
In the thus-constructed first exemplary embodiment of the invention, if the electric motor, the motor drive device, and its marginal device including a malfunction detection controller are in normal operation, the sum Vm of terminal voltages Vm1, Vm2 at the ends of the electric motor is approximately equal to the power voltage Vb due to the operation of the bridge circuit. If the respective switching elements are short-circuited, the sum Vm assumes a value which is approximately equal to or greater than 3xc2x7Vb/2 or a value which is approximately equal to or smaller than Vb/2. Further, even if the portions between respective ends of the electric motor and the grounded line or the power line are short-circuited, the sum Vm assumes a value which is approximately equal to or greater than 3xc2x7Vb/2 or a value which is equal to or smaller than Vb/2. As a result, according to the invention, since the malfunction judgment controller judges the occurrence of a malfunction when the sum of the terminal voltages of the electric motor is different from the power voltage by a predetermined value or more, various malfunctions as mentioned above are detected. Thus, it is possible to provide a suitable countermeasure against those malfunctions.
Further, a second exemplary embodiment of the invention is applied to a motor drive unit which controls the electric motor by using the bridge circuit as mentioned above. The motor drive unit has a malfunction judgment controller which judges the occurrence of a malfunction when the electric motor is out of operation and when the sum of the terminal voltages of the electric motor is different from the sum of voltage values which has been determined in advance based on the voltage values at the ends of the electric motor during a turned-off state of all the switching elements by a predetermined value or more.
In the thus-constructed second exemplary embodiment of the invention, if the electric motor, the motor drive device and its marginal device including the malfunction detection controller are in normal operation, the sum Vm of the terminal voltages Vm1, Vm2 at the ends of the electric motor is equal to a predetermined voltage in a turned-off state of all the switching elements. For example, if the electric motor is grounded at one end through a pull-down resistor without connecting the electric motor at another end to the power line through a pull-up resistor, the sum Vm is equal to a ground voltage xe2x80x9c0xe2x80x9d (hereinafter referred to as a first mode). Further, if at least one of the ends of the electric motor is connected to the power line through the pull-up resistor and at least one of the other ends of the electric motor is grounded through the pull-down resistor, the sum Vm is equal to a value which is twice as great as a predetermined value between the power voltage Vb and the ground voltage xe2x80x9c0xe2x80x9d (equal to the power voltage Vb if the pull-up resistor and the pull-down resistor assume the same resistance value) (hereinafter referred to as a second mode). In addition, if the electric motor is connected to the power line through the pull-up resistor without grounding the ends of the electric motor through the pull-down resistor, the sum Vm is equal to the power voltage 2xc2x7Vb (hereinafter referred to as a third mode).
In the first mode, while the electric motor is out of operation as mentioned above, if portions between the switching elements on the side of the power line of the bridge circuit and the power line have been short-circuited, or if portions between the ends of the electric motor and the power line have been short-circuited, the sum Vm is approximately equal to 2xc2x7Vb.
Further, in the second mode, while the electric motor is out of operation as mentioned above, if the switching elements of the bridge circuit have been short-circuited, the sum Vm is approximately equal to 2xc2x7Vb or xe2x80x9c0xe2x80x9d. Further, if portions between the ends of the electric motor and the power line or the grounded line have been short-circuited, the sum Vm is approximately equal to 2xc2x7Vb or xe2x80x9c0xe2x80x9d.
In addition, in the third mode, while the electric motor is out of operation as mentioned above, if portions between the switching elements on the grounded side of the bridge circuit and the grounded line have been short-circuited, or if portions between the ends of the electric motor and the grounded line have been short-circuited, the sum Vm is approximately equal to xe2x80x9c0xe2x80x9d.
As a result, according to the second exemplary embodiment of the invention, the malfunction judgment controller judges the occurrence of a malfunction when the detected sum of the terminal voltages of the electric motor is different from the sum of voltage values which has been determined in advance based on the voltage values at the ends of the electric motor during a turned-off state of all the switching elements by at least a predetermined value. Thus, various malfunctions as described above are detected. That is, a wide variety of malfunctions relating to the electric motor are detected, whereby it becomes possible to provide a suitable countermeasure against those malfunctions.
Furthermore, according to a third exemplary embodiment of the invention, the motor drive unit has a malfunction judgment controller which approximately sets the terminal voltages at the ends of the electric motor to a lower power voltage during a turned-off state of all the switching elements by connecting at least one of the ends of the electric motor to the power line through the pull-up resistor and grounding at least the other end of the electric motor through the pull-down resistor and which judges the occurrence of a malfunction when the sum of the terminal voltages of the electric motor is different from the power voltage by a predetermined value or more.
In the thus-constructed third exemplary embodiment of the invention, if the electric motor, the motor drive device, and its marginal circuit including the malfunction detection controller are in normal operation, when the electric motor is in operation, the sum Vm of the terminal voltages Vm1, Vm2 at the ends of the electric motor is approximately equal to the power voltage Vb due to the operation of the bridge circuit. Further, when the electric motor is out of operation, the sum Vm of the terminal voltages Vm1, Vm2 at the ends of the electric motor is approximately equal to the power voltage Vb due to the operation of the pull-up resistor and the pull-down resistor.
Further, while the electric motor is in operation, if the switching elements have been short-circuited, the sum Vm assumes a value which is approximately equal to or to greater than 3xc2x7Vb/2 or a value which is approximately equal to or smaller than Vb/2. Further, while the electric motor is in operation, if portions between the ends of the electric motor and the grounded line or the power line have been short-circuited, the sum Vm assumes a value which is approximately equal to or greater than 3xc2x7Vb/2 or a value which is approximately equal to or smaller than Vb/2. Further, while the electric motor is out of operation, if the switching elements of the bridge circuit have been short-circuited, the sum Vm is approximately equal to 2xc2x7Vb or xe2x80x9c0xe2x80x9d. Further, while the electric motor is out of operation, if portions between the ends of the electric motor and the power line or the grounded line have been short-circuited, the sum Vm is approximately equal to 2xc2x7Vb or xe2x80x9c0xe2x80x9d.
As a result, according to the third exemplary embodiment of the invention, the malfunction judgment controller judges the occurrence of a malfunction when the detected sum of the terminal voltages of the electric motor is different from the power voltage by at least a predetermined value. Thus, various malfunctions as mentioned above are detected. That is, a wide variety of malfunctions relating to the electric motor are detected, whereby it becomes possible to provide a suitable countermeasure against those malfunctions. Further, in this case, when the electric motor is out of operation, the sum of the terminal voltages at the ends of the electric motor is set equal to the power voltage by means of the pull-up resistor and the pull-down resistor. Thus, it is possible to simultaneously judge the occurrence of a malfunction based on one sort of judgment regardless of whether the electric motor is in operation or out of operation. Therefore, the judgment of a malfunction occurring in marginal devices of the motor drive unit can be made with ease.
Further, according to another exemplary embodiment of the invention, there is provided a method of detecting a malfunction for a motor drive unit which has a bridge circuit composed of four sides including switching elements, an electric motor whose ends are connected to a pair of terminals at diagonal positions of the bridge circuit, a power circuit which applies a power voltage to a pair of terminals by connecting one of the terminals at the other diagonal positions to a power line and grounding the other terminal, and a motor drive device which controls the electric motor by performing pulse width modulation control of the switching elements. In the method of detecting a malfunction, the sum of the terminal voltages of the electric motor is detected, and the occurrence of a malfunction in at least one of the bridge circuit, the electric motor and the motor drive device is judged if the sum of the terminal voltages of the electric motor is different from the power voltage by at least a predetermined value during operation of the electric motor.
Further, in a method of detecting a malfunction in accordance with still another exemplary embodiment of the invention, the sum of the terminal voltages of the electric motor is detected, and the occurrence of a malfunction in at least one of the bridge circuit, the electric motor and the motor drive device is judged when the electric motor is out of operation and when the sum of the terminal voltages of the electric motor is different from the sum of voltage values which has been determined in advance based on the voltage values at the ends of the electric motor during a turned-off state of all the switching elements by a predetermined value or more.
Further, in a method of detecting a malfunction in accordance with still another exemplary embodiment of the invention, terminal voltages at the ends of the electric motor are set to a lower power voltage during a turned-off state of all the switching elements by connecting at least one of the ends of the electric motor to the power line through a pull-up resistor and grounding at least the other of the ends of the electric motor through a pull-down resistor, and the sum of the terminal voltages of the electric motor is detected, and the occurrence of a malfunction in at least one of the bridge circuit, the electric motor and the motor drive device is judged if the sum of the terminal voltages of the electric motor is different from the power voltage by a predetermined value or more.